1. Field of the Invention
This invention relates to the field of computer software protection. More particularly, this invention relates to combating the making of unauthorized copies of software.
2. Background Information
Computer software, whether in the form of computer programs or data files, is a valuable asset. Much expense is involved in the production of such software, and yet, software is particularly vulnerable to theft. It is possible to make a copy of a piece of computer software in a matter of seconds using standard computer equipment and an appropriate medium such as a blank floppy disk. Once a copy is made the original is completely intact, and the unauthorized copy may be used by the thief without any payment to the software owner.
A large number of techniques have been proposed to combat the making of such unauthorized copies. Typically, these techniques concentrate on the prevention of the production of working copies of the software, e.g. by encryption, passwords or physical devices needed to enable use of the software. Examples of such techniques are described in British Published Patent Application No. 2154769, European Published Patent Application No. 302710, European Published Patent Application No. 67998 and International Published Patent Application No. WO 85/02310. Such techniques result in increased complexity, and while offering a degree of protection are, as with most forms of security, open to defeat by appropriate countermeasures. New security measures, particularly ones that can be simply and cheaply implemented, are desirable in trying to counteract unauthorlzed copying.